Catalyst for the polymerization of olefins

ABSTRACT

Catalyst system for the polymerization of olefins CH 2 ═CHR, wherein R is hydrogen or a hydrocarbon radical having 1-12 carbon atoms, comprising the product of the reaction between (a) a solid catalyst component comprising Mg, Ti, and halogen, (b) dimethylaluminium chloride (DMAC) and (c) an alkylaluinium compound, in which the molar ratio between (b) and (c) is lower than 10. This kind of catalyst system is particularly suitable for the preparation of copolymers of ethylene with α-olefins due to its high capacity for incorporating the comonomer while at the same time maintaining high yields.

The present invention relates to catalysts for the polymerization ofolefins CH₂═CHR, wherein R is hydrogen or a hydrocarbon radical having1-12 carbon atoms. In particular, the present invention relates to acatalyst obtained by reacting a solid catalyst component, based on Mg,Ti and halogen, with a particular pair of alkyl-Al compounds. This kindof catalyst is particularly suitable for the preparation of copolymersof ethylene with α-olefins due to its high capacity for incorporatingthe comonomer while at the same time maintaining high yields.

Accordingly, another object of the present invention is the use of saidcatalysts in a process for the copolymerization of olefins in order toproduce ethylene/α-olefin copolymers.

Linear low-density polyethylene (LLDPE) is one of the most importantproducts in the polyolefin field. Due to its characteristics, it findsapplication in many sectors and in particular in the field of wrappingand packaging of goods where, for example, the use of stretchable filmsbased on LLDPE constitutes an application of significant commercialimportance. LLDPE is commercially produced with liquid phase processes(solution or slurry) or via the more economical gas-phase process. Bothprocesses involve the widespread use of Ziegler Natta MgCl₂-supportedcatalysts that are generally formed by the reaction of a solid catalystcomponent, in which a titanium compound is supported on a magnesiumhalide, with an alkylaluminium compound.

In order to be advantageously usable in the preparation of LLDPE, saidcatalysts are required to show high comonomer incorporation propertiesand good comonomer distribution suitably coupled with high yields.

The requirement of high comonomer incorporation is particularlyimportant in the case of gas-phase production processes because the useof excessively large amounts of α-olefin in the feed mixture can causecondensation phenomena in the gas-phase reactor. Therefore, the use of acatalyst having a high capacity for incorporating the comonomer wouldmake it possible to lower the amount α-olefin monomer in the feed.

It is known in the art that the use of different co-catalysts canmodulate certain;properties of the solid catalyst component like, forexample, polymerization activity, ability to produce higher or lowermolecular weights polymers, comonomer distribution, etc. In particular,it is reported in the art that the use of dimethylaluminium chloridewith respect to a trialkylaluminium, would give catalysts capable ofproducing ethylene polymers with a broader Molecular Weight Distribution(MWD) and also capable of incorporating a higher amount of comonomer.However, all the above improvements are made redundant by the fact thatthe yields are dramatically decreased.

International patent application WO 95/17434 discloses a catalyst systemaimed at solving this problem. It is characterized by the use ofDMAC/trialkylaluminium (TAA) co-catalyst mixtures in molar ratios from30 to 300. Table 1 of said application shows that when the DMAC/TAAmolar ratio is higher than 30, a high Melt Flow Ratio (indicating abroad MWD) and a melt index in the range 10-20 are obtained. Theincorporation of a comonomer in this range of DMAC/TAA molar ratioappears to increase slightly as a function of the TAA content (it passesfrom 2.1% with the use of pure DMAC to 2.3% with the use of a DMAC/TAAmolar ratio of 30). The yields however are very low in this range ifcompared with the TAA alone. In particular, the activity of the bestinvention example of Table 1 (Example 4) is about 160 times lower thanthe activity obtained with triethylaluminium (TEAL) alone. On the otherhand, said application shows that when DMAC/TAA molar ratios lower than30 are used, the Molecular Weight of the polymer decreases (the meltindex in the range 20-60), the MWD becomes narrower (Melt Flow Ratioslower than 30 are obtained) and, most importantly, at the same time theincorporation of comonomer does not increase (the value of 2.3% remainsconstant). All the above drawbacks are not offset by the slight increasein activity which, for a DMAC/TEAL molar ratio of 20, remains about 85times lower than that for TEAL alone.

Contrary to the strong suggestion of using a large excess of DMAC withrespect to the alkylaluminium, we have surprisingly discovered that theuse of DMAC/alkylaluminum compound co-catalyst mixtures having lowermolar ratios gives catalysts with completely unexpected properties. Saidcatalysts in fact have a very high capacity for incorporating theco-monomer while at the same time displaying activity which is higherthan that obtainable by the use of the aluminium alkyl alone.

Accordingly, an object of the present invention is a catalyst systemcomprising the product of the reaction between (a) a solid catalystcomponent comprising Mg, Ti, halogen and optionally an electron donorcompound, (b) dimethylaluminium chloride (DMAC) and (c) an compound inwhich the molar ratio between (b) and (c) is lower than 10.

In the reaction with component (a), the DMAC and the alkyaluminiumcompound are preferably used in molar ratios from 0.01 to 5 and morepreferably between 0.3 and 3.

The alkylaluminium compound can be selected from the compounds offormula AlR¹ _(3−y)H_(y) where y is from 0 to 2 and R¹ is a hydrocarbongroup having from 1 to 15 carbon atoms. Preferably, the alkylaluminiumcompound (c) is selected from those of the above formula in which y is 0and R¹ is a C2-C10 alkyl radical. Examples of suitable aluminium alkylcompounds are di-(2,4,4-trimethylpentyl)aluminium hydride,triethylaluminum, triisopropylaluminum, triisobutylaluminum,tri-n-hexylaluminum and tri-(2,4,4-trimethylpentyl)aluminium. The use oftriethyl- or triisobutylaluminium is especially preferred.

As explained above, the component (a) of the invention is a solidcatalyst component comprising Ti, Mg and halogen. In particular, thesaid catalyst component comprises a titanium compound supported on amagnesium halide. The magnesium halide is preferably MgCl₂ in activeform, which is widely known from the patent literature as a support forZiegler-Natta catalysts. Patents U.S. Pat. Nos. 4,298,718 and 4,495,338were the first to describe the use of these compounds in Ziegler-Nattacatalysis. It is known from these patents that the magnesium dihalidesin active form used as support or co-support in components of catalystsfor the polymerization of olefins are characterized by X-ray spectra inwhich the most intense diffraction line that appears in the spectrum ofthe non-active halide is diminished in intensity and is replaced by ahalo whose maximum intensity is displaced towards lower angles relativeto that of the most intense line.

The preferred titanium compounds are those of formulaTi(OR²)_(n−y)X_(y), where X is halogen, preferably chlorine, n is thevalence of titanium, y is a number between 0 and n, and the R² groups,which may be identical or different, are hydrocarbon radicals havingfrom 1 to 10 carbon atoms. Particularly preferred titanium compounds areTiCl₄, TiCl₃, titanium (IV) butoxide and titanium (IV) isopropoxide,trichlorobutoxy titanium (IV) and dichlorobutoxytitanium (III).

The preparation of the solid catalyst component can be carried outaccording to several methods. According to one of these methods, theproduct obtained by co-milling the magnesium chloride in an anhydrousstate and the titanium compound is treated with halogenated hydrocarbonssuch as 1,2-dichloroethane, chlorobenzene, dichloromethane, etc. Thetreatment is carried out for a time between 1 and 4 hours and at atemperature ranging from 40° C. to the boiling point of the halogenatedhydrocarbon. The product obtained is then generally washed with inerthydrocarbon solvents such as hexane.

According to another method, magnesium dichloride is pre-activatedaccording to well-known methods and then treated with an excess of Ticompound at a temperature of about 80 to 135° C. The treatment with theTi compound is repeated and the solid is washed with hexane in order toeliminate any non-reacted Ti compound.

A further method comprises the reaction between magnesium alkoxides orchloroalkoxides (in particular chloroalkoxides prepared according toU.S. Pat. No. 4,220,554) and an excess of TiCl₄ in solution at atemperature of about 80 to 120° C.

According to a preferred method, the solid catalyst component can beprepared by reacting a titanium compound of the formula disclosed abovewith a magnesium chloride derived from an adduct of formula MgCl₂.pR³OH,where p is a number between 0.1 and 6, preferably from 2 to 3.5, and R³is a hydrocarbon radical having 1-18 carbon atoms. The adduct can besuitably prepared in spherical form by mixing alcohol and magnesiumchloride in the presence of an inert hydrocarbon which is immisciblewith the adduct, operating under stirred conditions at the melting pointof the adduct (100-130° C.). The emulsion is then quickly quenched,thereby causing the solidification of the adduct in the form ofspherical particles. Examples of spherical adducts prepared according tothis procedure are described in U.S. Pat. Nos. 4,399,054 and 4,469,648.

The adduct thus obtained can be reacted directly with the Ti compound,preferably TiCl₄, or it can be subjected beforehand to controlledthermal dealcoholation (80-130° C.) so as to obtain an adduct in whichthe number of moles of alcohol is generally lower than 3, preferablybetween 0.1 and 2.5. The reaction with the Ti compound can be carriedout by suspending the adduct (optionally dealcoholated) in the liquid Ticompound (generally at 0° C.); the mixture is heated to 80-130° C. andkept at this temperature for 0.5-2 hours. The treatment with the Ticompound can be carried out one or more times.

The preparation of catalyst components in spherical form according tothis procedure is described for example in European Patent ApplicationsEP-A-395083, EP-A-553805 and WO 98/44001. According to a variation ofthe method described above the preparation of the solid catalystcomponents can comprise (i) reacting a compound MgCl₂.mROH, wherein 0.3≦m ≦1.7 and R is an alkyl, cycloalkyl or aryl radical having 1-12 carbonatoms, with a titanium compound of the formula Ti(OR²)_(n−y)X_(y), givenabove; (ii) reacting the product obtained from (i) with an Al-alkylcompound and (iii) reacting the product obtained from (ii) with atitanium compound of the formula Ti(OR^(II))_(n)X_(y−n), in which n, y,X and R^(II) have the meanings explained above. As mentioned above, thecompound MgCl₂.mROH can be prepared by thermal dealcoholation of adductsMgCl₂.pEtOH, having a higher alcohol content. Preferred titaniumcompounds used in step (i) and (iii) are titanium tetrahalides, inparticular TiCl₄ Particularly preferred in step (ii) is the use of thetrialkyl aluminum compounds such as those disclosed above.

According to another embodiment, the MgCl₂.pR³OH adduct is firstthermally dealcoholated according the procedure described above andsuccessively placed in contact with reactive compounds capable ofremoving the alcohol. Suitable reactive compounds are, for example,alkyl-Al compounds or SiCl₄. The adduct thus obtained is then reactedwith a titanium compound in order to obtain the final solid catalystcomponent. The preparation of catalyst components in spherical formaccording to this procedure is described for example in EP-A-553806, andEP-A-601525.

The solid catalyst components obtained with methods including the use ofMgCl2.alcohol adducts show a surface area (by the B.E.T. method)generally of between 20 and 500 m²/g and preferably between 50 and 400m²/g, and a total porosity (by the B.E.T. method) of higher than 0.2cm³/g, preferably between 0.2 and 0.6 cm³/g. The porosity (Hg method)due to pores with a radius up to 10.000Å generally ranges from 0.3 to1.5 cm³/g, preferably from 0.45 to 1 cm³/g.

In the methods disclosed above the titanium compound to be supported onthe magnesium dihalide is normally pre-formed. Alternatively, it canalso be produced in-situ, for example by the reaction of a titaniumtetrahalide, in particular TiCl₄, with an alcohol R²OH or with titaniumalkoxides having the formula Ti(OR²)₄. When the preparation of thecatalyst component includes the use of an MgCl₂.pR³OH adduct, thetitanium compound can be obtained by the reaction of a titaniumtetrahalide, in particular TiCl₄, with the OH groups of the residualalcohol present in a combined form in said magnesium dihalide.

According to another embodiment, the final titanium compound can beobtained by the reaction of a titanium tetraalkoxide with halogenatingcompounds such as, for instance, SiCl₄, AlCl₃ or chlorosilanes.

In some instances it is convenient that the titanium compound be reducedto a valence of lower than 4. For example, titanium haloalkoxides with avalence of lower than 4 can also be formed by means of the reaction oftitanium tetraalkoxides with mixtures of halogenating and reducingcompounds like, for example, silicon tetrachloride andpolyhydrosiloxanes. Moreover, it is also possible to use a halogenatingagent which simultaneously acts as a reducing agent, such as, forinstance, an alkyl-Al halide.

As mentioned above, the solid catalyst component to be used incombination with the DMAC/alkylaluminum mixture may comprise an electrondonor compound (internal donor), preferably selected from ethers,esters, amines and ketones.

Said compound is necessary when the component is used in thestereoregular (co)polymerization of olefins such as propylene, 1-buteneor 4-methyl-1-pentene. In particular, the internal electron donorcompound can be suitably selected from the alkyl, cycloalkyl or arylesters of polycarboxylic acids, such as for example esters of phthalic,succinic and maleic acid, in particular n-butyl phthalate, diisobutylphthalate, di-n-octyl phthalate and di-n-hexyl phthalate diethyl2,3-diisopropylsuccinate.

Other electron donor compounds advantageously usable are the1,3-diethers of the formula:

wherein R^(I) and R^(II), which may be identical or different, arealkyl, cycloalkyl, aryl radicals having 1-18 carbon atoms or hydrocarbonradicals that can be linked together to form condensed structures, andR^(III) and R^(IV), which may be identical or different, are alkylradicals having 1-4 carbon atoms.

The electron donor compound is generally present in a molar ratio withrespect to the magnesium from 1:4 to 1:20.

As previously explained, the catalysts of the invention are obtained byreacting (a) a solid catalyst component comprising Mg, Ti, halogen andoptionally an electron donor compound, with (b) dimethylaluminiumchloride (DMAC) and (c) an alkylaluminium compound in which the molarratio between (b) and (c) is lower than 10.

The reaction between the three components can be carried out in severaldifferent ways, depending on which certain properties of the catalystscan be particularly enhanced with respect to the others. On the basis ofthe following guidelines, the reaction conditions can be properlyselected by a person skilled in the art in order to obtain the catalysthaving the required balance of properties. For example, a catalysthaving a very high activity and a relatively lower capacity forincorporating the co-monomer is obtained by first placing the components(a) and (c) in contact and then reacting the product thus obtained withthe component (b). In this case, the component (b) can be added directlyto the polymerization reactor. Catalysts having a better a balancebetween activity and good capacity for incorporating the co-monomer areobtainable by placing the component (a) in contact with a mixture of (b)and (c) or, preferably, by first placing the components (a) and (b) incontact and then reacting the product thus obtained with the component(c). Also in this case, the component (c) or the mixture of (b) and (c)can be added directly to the polymerization reactor. We also found thatif the addition of component (c) is in some way delayed, for examplebecause a polymerization diluent and possibly also the monomer are addedbefore, it is possible to obtain a catalyst displaying an exceptionalcapacity for incorporating the comonomer together with a relativelylower polymerization activity.

In all the above-disclosed methods, the DMAC and alkylaluminum compoundsare normally used in solution or suspension in a hydrocarbon medium suchas propane, pentane, hexane, heptane, benzene, toluene, or inhalogenated hydrocarbons such as dichloromethane, dichloroethane andCCl₄.

The component (a) can be used to prepare the catalyst composition asobtained directly from its preparation process. Alternatively, it can bepre-polymerized with ethylene and/or α-olefins before being used in themain polymerization process. This is particularly preferred when themain polymerization process is carried out in the gas phase. Inparticular, it is especially preferred to pre-polymerize ethylene ormixtures thereof with one or more a-olefins, said mixtures containing upto 20 mol % of α-olefin, forming amounts of polymer from about 0.1 g pergram of solid component up to about 100 g per gram of solid catalystcomponent. The pre-polymerization step can be carried out attemperatures from 0 to 80° C., preferably from 5 to 50° C., in theliquid or gas phase. The pre-polymerization step can be performedin-line as a part of a continuous polymerization process or separatelyin a batch process. The batch pre-polymerization of the catalyst of theinvention with ethylene in order to produce an amount of polymer rangingfrom 0.5 to 20 g per gram of catalyst component is particularly,preferred. The prepolymerized catalyst component can also be subject toa further treatment with a titanium compound before being used in themain polymerization step. In this case the use of TiCl₄ is particularlypreferred. The reaction with the Ti compound can be carried out bysuspending the prepolymerized catalyst component in the liquid Ticompound optionally in mixture with a liquid diluent; the mixture isheated to 60-120° C. and kept at this temperature for 0.5-2 hours.

The presence of a pre-polymerization step makes it possible to react thecomponents (a) to (c) of the present invention according to differentembodiments. In one of them, the component (a) is prepolymerized byusing only an alkylaluminum compound as a cocatalyst. The so obtainedprepolymerized catalyst component can then be used in the mainpolymerization process together with the DMAC/alkylaluminum mixture ofthe invention thereby obtaining the described advantages with respect toa polymerization step carried out only with the alkylaluminium compound.

According to another embodiment the catalyst component (a) is reacteddirectly in the prepolymerization step with a mixture of DMAC andalkyaluminum used as co-catalyst. The so obtained prepolymerizedcatalyst component can then be used in the main polymerization processin combination with a cocatalyst that can be either an alkylaluminiurncompound or a DMAC/alkylaluminium mixture. The use ofDMAC/alkylaluminium mixture is preferred. In case an alkylaluminiumcompound is used as cocatalyst however, the skilled in the art shouldavoid any washing of the prepolymerized catalyst component in order topreserve its ability to give the advantages described above. Asmentioned, the main polymerization process using the catalyst of theinvention can be carried out according to known techniques either inliquid or gas phase using, for example, the known technique of thefluidized bed or under conditions wherein the polymer is mechanicallystirred. Preferably, the process is carried out in the gas phase.

Examples of gas-phase processes wherein it is possible to use thecatalysts of the invention are described in WO 92/21706, U.S. Pat. No.5,733,987 and WO 93/03078. These processes comprise a pre-contact stepof the catalyst components, a pre-polymerization step and a gas phasepolymerization step in one or more reactors in a series of fluidized ormechanically stirred bed. The catalysts of the present invention areparticularly suitable for preparing linear low density polyethylenes(LLDPE, having a density lower than 0.940 g/cm³) and very-low-densityand ultra-low-density polyethylenes (VLDPE and ULDPE, having a densitylower than 0.920 g/cm³, to 0.880 g/cm³) consisting of copolymers ofethylene with one or more alpha-olefins having from 3 to 12 carbonatoms, having a mole content of units derived from ethylene of higherthan 80%. However, they can also be used to prepare a broad range ofpolyolefin products including, for example, high density ethylenepolymers (HDPE, having a density higher than 0.940 g/cm³), comprisingethylene homopolymers and copolymers of ethylene with alpha-olefinshaving 3-12 carbon atoms; elastomeric copolymers of ethylene andpropylene and elastomeric terpolymers of ethylene and propylene withsmaller proportions of a diene having a content by weight of unitsderived from ethylene of between about 30 and 70%; isotacticpolypropylenes and crystalline copolymers of propylene and ethyleneand/or other alpha-olefins having a content of units derived frompropylene of higher than 85% by weight; impact resistant polymers ofpropylene obtained by sequential polymerization of propylene andmixtures of propylene with ethylene, containing up to 30% by weight ofethylene; copolymers of propylene and 1-butene having a number of unitsderived from 1-butene of between 10 and 40% by weight.

The following examples are given in order to further describe thepresent invention in a non-limiting manner.

CHARACTERIZATION

The properties are determined according to the following methods:

Melt Index: measured at 190° C. according to ASTM D-1238 condition “E”(load of 2.16 Kg) and “F” (load of 21.6 Kg);

The ratio between MI F and MI E (indicated as F/E) is thus defined asthe melt flow ratio (MFR).

Fraction soluble in xylene. The solubility in xylene at 25° C. wasdetermined according to the following method: About 2.5 g of polymer and250 ml of o-xylene were placed in a round-bottomed flask provided withcooler and a reflux condenser and kept under nitrogen. The mixtureobtained was heated to 135° C. and was kept under stirring for about 60minutes. The final solution was allowed to cool to 25° C. undercontinuous stirring, and was then filtered. The filtrate was thenevaporated in a nitrogen flow at 140° C. to reach a constant weight. Thecontent of said xylene-soluble fraction is expressed as a percentage ofthe original 2.5 grams.

Thermal analysis: Calorimetric measurements were performed by using aMettler DSC differential scanning calorimeter. The instrument wascalibrated with indium and tin standards. The weighed sample (5-10 mg),was sealed into aluminium pans, heated to 200° C. and kept at thattemperature for a time long enough (5 minutes) to allow a completemelting of all the crystallites. Successively, after cooling at 20°C./min to −20° C., the peak temperature was assumed as crystallizationtemperature (Tc). After standing for 5 minutes at 0° C., the sample washeated to 200° C. at a rate of 10° C./min. In this second heating run,the peak temperature was assumed as the melting temperature (Tm) and thearea as the global melting enthalpy (AH).

Comonomer Content

1-Butene was determined via Infrared Spectrometry.

The α-olefins higher than 1-butene were determined via ¹H NMR analysis.The total area of the ¹H NMR spectrum (between 2.5 and 0.5 ppm) wasdivided in two regions:

A, between 2.5-1.1 ppm for CH₂ and CH

B, between 1.1-0.5 ppm for CH₃

The copolymer composition was then calculated using the followingequations:${{Cn}\quad \left( {{mol}.\quad \%} \right)} = {\frac{I_{B}/3}{Tot} \cdot 100}$${E\quad \left( {{mol}.\quad \%} \right)} = {\frac{\left\{ {I_{A} - \left\lbrack {\left( {I_{B}/3} \right) \cdot \left( {{2n} - 3} \right)} \right\rbrack} \right\}/4}{Tot} \cdot 100}$

where:

Tot=Cn+E

n=number of 1-olefin C-atoms

I_(A), I_(B)=integrals of the regions A and B respectively.

Effective density: ASTM-D 1505

EXAMPLES Preparation of the Spherical Support (MgCl₂/EtOH Adduct)

The adduct of magnesium chloride and alcohol was prepared according tothe method described in Example 2 of U.S. Pat. No. 4,399,054, butoperating at 2000 rpm instead of 10,000 rpm. The adduct containingapproximately 3 mol of alcohol had an average size of approximately 60μm, with a dispersion range of approximately 30-90 μm.

Preparation of the Solid Component

The spherical support, prepared according to the general method, wassubjected to thermal treatment, under nitrogen flow, within thetemperature range of 50-150° C., until spherical particles having aresidual alcohol content of about 35 wt. % (1.1 mol of alcohol per moleof MgCl₂) were obtained.

600 g of this support, in suspension with 3 dm³ of anhydrous heptane,were loaded into a 5 dm³ reactor. With stirring at 20° C., 260 g of TEALdissolved in heptane (100 g/dm³) were slowly added: The temperature wasraised to 40° C. over 60 minutes and kept constant for 120 minutes.Stirring was discontinued, settling was allowed to occur and the clearphase was removed. The residue was washed 3 times with anhydrous heptaneand then dispersed with 3 dm³ of anhydrous heptane. Stirring wasinitiated and at 20° C., over a period of 60 minutes, the reactionproduct was fed with 1100 g of Ti(OBu)₄ and 850 g of SiCl₄ (solutionobtained at 25° C.).

The temperature was raised to 60° C. over 50 minutes and kept constantfor 2 hours, then the liquid phase was separated out by settling andsiphoning. Seven washes with heptane (3 dm³ each time) were carried out,3 thereof at 60° C. and 4 at room temperature. The component inspherical form was vacuum-dried at 50° C.

The catalyst characteristics were as follow:

Ti (total) 8.1 wt. % Mg 11.38 wt. % Cl 46.7 wt. % Si 1.5 % wt Al(residual) 0.15 wt. % —Oet 7.2 wt. % —OBu 15.9 wt. % residual solvent 4wt. %

Comparative Example 1 and Example 1-3

A 4.5 L stainless-steel autoclave equipped with a helical magneticstirrer, temperature and pressure indicator, feed line for ethylene,propane, hydrogen, 1-butene and a steel vial for the injection of thecatalyst was used and purified by flushing ethylene at 80° C. andwashing with propane.

In the following order, 11.4 ml of 10% (by wt/vol) TEAL/hexane solution(or 10 mmol of the TEAL/DMAC mixture, previously prepared by placing incontact the two compounds in the molar ratio indicated in table 1), andthe solid catalyst prepared according to the above-disclosed procedurewere mixed together at room temperature, matured for 5 minutes andintroduced in the empty reactor in a stream of propane. The autoclavewas then closed and 940 g of propane were introduced, after which thetemperature was raised to 75° C. (10 minutes) with simultaneousintroduction of 80 g of ethylene (6.8 bar, partial pressure) and 78 g(314 ml) of 1-butene. At the end, 1.45 bar of hydrogen (partialpressure) were added. Under continuous stirring, the total pressure wasmaintained at 75° C. for 120 minutes by feeding an ethylene/1-butenemixture (9:1 molar ratio). At the end, the reactor was depressurized andthe polymerization stopped by injection of CO. The polymer recovered wasdried under vacuum at 60° C. The results of the polymerization runs andthe characteristics of the polymers are reported in Table 1.

Example 4

The polymerization was carried out according to the procedure describedin the previous example, the only difference being that the solidcatalyst was matured for 5 minutes only with 5 mmol of TEAL solution,and 5 mmol of DMAC were introduced into the empty autoclave. The resultsof the polymerization runs and the characteristics of the polymer arereported in Table 1.

Example 5

The polymerization was carried out according to the procedure describedin Example 1, the only difference being that the solid catalyst wasmatured for 5 minutes only with 5 mmol of DMAC solution, and 5 mmol ofTEAL were introduced into the empty autoclave.

The results of the polymerization runs and the characteristics of thepolymer are reported in Table 1.

Example 6

The polymerization was carried out according to the procedure describedin Example 1, the only difference being that the solid catalyst wasmatured for 5 minutes only with 5 mmol of DMAC solution, and 5 mmol ofTEAL were injected into the autoclave after the propane diluent at 30°C. by using an excess pressure of ethylene. The results of thepolymerization runs and the characteristics of the polymer are reportedin Table 1.

Example 7

A 4.5 L stainless-steel autoclave equipped with a helical magneticstirrer, temperature and pressure indicator, feed line for ethylene,propane, hydrogen, 1-butene and a steel vial for the injection of thecatalyst was used and purified by flushing ethylene at 80° C. andwashing with propane.

In the following order, 3.8 ml of 10%, by wt/vol (3.33 mmol), ofTEAL/hexane solution and 6.2 ml of 10%, by wt/vol (6.7 mmol), ofDMAC/hexane solution, were previously prepared and then 19 mg of thesolid catalyst of Example 1 (Ti content, 8.1 wt. %), were mixed togetherat room temperature, matured for 5 minutes and introduced into the emptyreactor in a stream of propane. The autoclave was then closed and 940 gof propane were introduced, after which the temperature was raised to75° C. (10 minutes) with simultaneous introduction of 98 g of ethylene(8.3 bar, partial pressure) and 165 g (293 ml) of 1-butene. At the end,1.5 bar of hydrogen (partial pressure) were added. Under continuousstirring, the total pressure was maintained at 75° C. for 60 minutes byfeeding an ethylene/1-butene mixture (9:1 molar ratio). At the end, thereactor was depressurized and the polymerization stopped by injection ofCO. The resulting polymer was then dried under vacuum at 60° C. 340 g.of polymer were recovered. The results of the polymerization runs andthe characteristics of the polymers are reported in Table 1.

Comparative Example 2

A 4.5 L stainless-steel autoclave equipped with a helical magneticstirrer, temperature and pressure indicator, feed line for ethylene,propane, hydrogen, 1-butene and a steel vial for the injection of thecatalyst was used and purified by flushing ethylene at 80° C. andwashing with propane.

In the following order, 18.5 ml of 10%, by wt/vol (20 mmol), ofDMAC/hexane solution and 87.5 mg of the solid catalyst of Example 1 (Ticontent, 8.1 wt. %), were mixed together at room temperature, maturedfor 5 minutes and introduced into the empty reactor in a stream ofpropane. The autoclave was then closed and 940 g of propane wereintroduced, after which the temperature was raised to 75° C. (10minutes) with simultaneous introduction of 98 g of ethylene (8.3 bar,partial pressure) and 165 g (293 ml) of 1-butene. At the end, 3.1 bar ofhydrogen (partial pressure) were added. Under continuous stirring, thetotal pressure was maintained at 75° C. for 60 minutes by feeding anethylene/1-butene mixture (9:1 molar ratio). At the end, the reactor wasdepressurized and the polymerization stopped by injection of CO. Theresulting polymer was dried under vacuum at 60° C. The results of thepolymerization runs and the characteristics of the polymers are reportedin Table 1.

Comparative Examples 3-5 and Examples 8-10

A 260 mL glass autoclave equipped with a magnetic stirrer, temperatureand pressure indicator, and feed line for ethylene was used and purifiedand flushed with ethylene at 35° C. 120 ml of heptane and 30 ml of the1-olefin indicated in Table 2 were introduced at room temperature.

The catalytic system was prepared separately in 10 ml (final volume) ofheptane by consecutively introducing 1.5 ml of 10%, by wt/vol,alkyaluminum/heptane solution (or 1.31 mmol of the alkyaluminum/DMACmixture, previously prepared by placing in contact the two aluminiumalkyl solutions in the molar ratio indicated in Table 2), and the solidcatalyst of Example 1 (Ti content, 8.1 wt. %) After stirring for 5minutes, the solution, was introduced into the autoclave under a streamof ethylene, the reactor was closed, the temperature was raised to 70°C. and pressurized to 4.0 barg. The total pressure was kept constant byfeeding ethylene.

After 60 minutes, the polymerization was stopped by cooling anddegassing the reactor and by introducing 1 ml of methanol. The polymerobtained was washed with acidic methanol and then with methanol, anddried in an oven at 60° C. under vacuum. The polymerization results andthe related polymer characteristics are reported in Table 2.

Comparative Example 6 and Example 11 Preparation of the Pre-polymer

A 260 mL glass autoclave equipped with a magnetic stirrer, temperatureand pressure indicator, and feeding line for ethylene was used andpurified by fluxing ethylene at 35° C. At room temperature wereintroduced 120 ml of heptane containing 10.5 mmol. of TEAL The catalyticsystem was prepared separately in 20 ml (final volume) of heptane byconsecutively introducing 2 ml of 10% by wt/vol, TEAL/heptane solutionand 6.8 g of the solid catalyst described in example 1. The suspension,was introduced into the autoclave under nitrogen flow, the reactor wasclosed and after 10 minutes stirring at 25° C., was pressurized with 0.2bar of ethylene. The total pressure was kept constant by feedingethylene to reach a conversion of 1(about 3 h) The polymerization wasstopped by interrupting the ethylene feeding, the slurry was thenfiltered under nitrogen atmosphere and the residue was washed with dryhexane and dried under vacuum. Finally, 14.7 g of prepolymer (conversionof 1.17 g/g_(cat)) were obtained.

Polymerization with the pre-polymerized catalyst

The polymerization was carried out according to the procedure describedin example 8 with the only differences that was used a polymerizationtemperature of 75° C. instead of 70° C. The polymerization conditions,the polymer amount and the related characteristics are reported in Table3.

Example 12-13 Preparation of the Pre-polymer

The prepolymer was prepared according to the same procedure disclosed inexample 11 with the difference that instead of TEAL was used a the samemolar amounts of a mixture DMAC/TEAL having a molar ratio of 1. Thepre-polyrner (14.3 g) recovered was used in the subsequentcopolymerization step without being washed.

Polymerization with the Pre-polymerized Catalyst

The polymerization was carried out according to the procedure describedin Example 11. The polymerization conditions, the polymer amount and therelated characteristics are reported in Table 3.

Comparative Example 7 and Example 14 Preparation of the Pre-polymer

The prepolymer was prepared according to the same procedure disclosed inexample 12 with the difference that at the end of the procedure the 19.4g obtained were washed with dry hexane and then dried under vacuum.

Polymerization with the Pre-polymerized Catalyst

The polymerization was carried out according to the procedure describedin Example 11. The polymerization conditions, the polymer amount and therelated characteristics are reported in Table 3.

Comparative Example 8 and Example 15 Preparation of Solid CatalystComponent

The spherical support, prepared according to the general methoddescribed in ex. 2 of U.S. Pat. No. 4,399,054 (but operating at 3000 rpminstead of 10000) was subjected to thermal treatment, under nitrogenflow, within the temperature range of 50-150° C., until sphericalparticles having a residual alcohol content of about 35 wt. % (1.1 molof alcohol per mol of MgCl₂) were obtained.

16 g of this support were charged, under stirring at 0° C., to a 750 cm³reactor containing 320 cm³ of pure TiCl₄ and 3.1 cm³ ofdiisobutylphtalate, were slowly added and the temperature was raised to100° C. in 90 minutes and kept constant for 120 minutes. Stirring wasdiscontinued, settling was allowed to occur and the liquid phase wasremoved at the temperature of 80° C. Further 320 cm³ of freshly TiCl₄were added and the temperature was raised to 120° C. and kept constantfor 60 minutes. After 10 minutes settling the liquid phase was removedat the temperature of 100° C. The residue was washed with anhydrousheptane (300 cm³ at 70° C. then 3 times (250 cm³ each time) withanhydrous hexane at 60° C. and further 4 at ambient temperature. Thecomponent in spherical form was vacuum dried at 50° C.

The catalyst characteristics were the following:

Ti  2.3 wt. % Mg 18.7 wt. % Cl 60.7 wt. % diisobutylphtalate  4.4 wt. %

Ethylene/1-Butene Polynerization

4.0 liter stainless-steel autoclave equipped with a magnetic stirrer,temperature, pressure indicator, feeding line for ethylene, propane,1-butene, hydrogen, and a steel vial for the injection of the catalyst,was purified by fluxing pure nitrogen at 70° C. for 60 minutes. It wasthen washed with propane, heated to 75° C. and finally loaded with 800 gof propane, 1-butene (as reported in table 4), ethylene (7.0 bar,partial pressure) and hydrogen (2.0 bar, partial pressure).

In a 100 cm³ three neck glass flask were introduced in the followingorder, 50 cm³ of anhydrous hexane, 9.6 cm³ of 10% by wt/vol,aluminumalkyl/hexane solution (or the amount of aluminumalkyl/DMACmixture indicated in table 4) and the solid catalyst component preparedas described above.

They were mixed together and stirred at room temperature for 20 minutesand then introduced in the reactor through the steel vial by using anitrogen overpressure.

Under continuous stirring, the total pressure was maintained constant at75° C. for 120 minutes by feeding ethylene. At the end the reactor wasdepressurised and the temperature was dropped to 30° C. The recoveredpolymer was dried at 70° C. under a nitrogen flow and weighted. Thecharacteristics of the polymer obtained are reported in Table 4.

Comparative Example 9 and Example 16 Preparation of Solid CatalystComponents

Into a 500 mL four-necked round flask, purged with nitrogen, 250 mL ofTiC₄ were introduced at 0° C. While stirring, 10.0 g of microspheroidalMgCl₂.2.8C₂H₅OH (prepared according to the method described in ex.2 ofU.S. Pat. No. 4,399,054 but operating at 3000 rpm instead of 10000 rpm)and 7.4 mmol of diethyl 2,3-diisopropylsuccinate were added. Thetemperature was raised to 100° C. and maintained for 120 min. Then, thestirring was discontinued, the solid product was allowed to settle andthe supernatant liquid was siphoned off. Then 250 mL of fresh TiCl₄ wereadded. The mixture was reacted at 120° C. for 60 min and, then, thesupernatant liquid was siphoned off. The solid was washed six times withanhydrous hexane (6×100 mL) at 60° C. Finally, the solid was dried undervacuum and analyzed.

The catalyst characteristics were the following:

Ti  3.3 wt. % Mg 16.95 wt. % diethyl 2,3-diisopropylsuccinate  13.5 wt.%

Ethylene/1-butene Polymerization

The same procedure disclosed in Example 15 was used with the onlydifference that cyclohexylmethyl-dimethoxysilane was used as externaldonor in such an amount to give an Al/donor molar ratio of 15. Thecharacteristics of the polymer obtained are reported in Table 5.

Comparative Example 10 and Example 17

The polymerization was carried out according to the procedure describedin Example 8 with the only difference that DIOAH(di-(2,4,4-trimethylpentyl)aluminium hydride) was used in place of TEALand that the solid catalyst component was prepared according to theprocedure described in Ex.15. The polymerization conditions, the polymeramount and the related characteristics are reported in Table 5.

Example 18

The polymerization was carried out according to the procedure describedin Example 1 with the only difference that DIOAH(di-(2,4,4-trimethylpentyl)aluminium hydride) was used in place of TEALand that the solid catalyst component was prepared according to theprocedure described in Ex. 15. The polymerization conditions, thepolymer amount and the related characteristics are reported in Table 5.

Comparative Example 11 and Example 19 Preparation of the Solid Component

The spherical support, prepared according to the general methodunderwent a thermal treatment, under N₂ stream, over a temperature rangeof 50-150° C. until spherical particles having a residual alcoholcontent of about 25% (0.69 mole of alcohol for each MgCi₂ mole) wereobtained.

Into a 72 1 steel reactor provided with stirrer, 44 liters of TiCl at 0°C. and whilst stirring 2200 g of the support were introduced. The wholewas heated to 130° C. over 60 minutes and these conditions weremaintained for a further 60 minutes. The stirring was interrupted andafter 30 minutes the liquid phase was separated from the settled solid.Thereafter 4 washings with anhydrous hexane (about 22 liters) wereperformed two of which were carried out at 80° C. and two at roomtemperature.

Then, after the addiction of 31 liters of anhydrous hexane, 11 liters ofa solution of tris(2,4,4-trimethyl-pentyl)aluminum (Tioa) in hexane (100g/l) were introduced at room temperature into the reactor and stirredfor 30 minutes. The liquid phase was separated from the settled solidthat was washed with 22 liters of hexane and with 22 liters of heptane(twice for each other) at room temperature.

Thereafter a further treatment with 44 liters of TiCl4 was performed inthe same condition with respect to the first one, and after 4 washingswith anhydrous hexane, 2200 g of the spherical solid component wereobtained. After drying under vacuum at about 50° C., the solid showedthe following characteristics:

Total titanium  4.6% (by weight) Ti^(III)  0.6% (by weight) Al 0.11% (byweight) Mg 17.0% (by weight) Cl 73.4% (by weight) OEt  0.3% (by weight)

Polymerization

The polymerization was carried out according to the procedure describedin Example 8. The polymerization conditions, the polymer amount and therelated characteristics are reported in Table 6.

Comparative Example 12 and Example 20 Preparation of Solid CatalystComponent

10.0 g of microspheroidal MgCl₂.2.8C₂H₅OH (prepared according to themethod described in ex.2 of U.S. Pat. No. 4,399,054 but operating at3,000 rpm instead of 10,000) were subject to thermal dealcoholationcarried out at increasing temperatures from 30 to 95° C. and operatingin nitrogen current until a molar ratio EtOH/MgCl₂ of about 1 wasobtained.

The so obtained adduct was poured into a 500 ml four-necked round flask,purged with nitrogen, which contained 250 ml of TiCl4 introduced at 0°C. The flask was heated to 40° C. and 6 mmoles of diisobutylphthalate(DIBP) were thereupon added. The temperature was raised to 100° C. andmaintained for two hours, then the stirring was discontinued, the solidproduct was allowed to settle and the supematant liquid was siphonedoff. The treatment with TiCl₄ was repeated and the solid obtained waswashed six times with anhydrous hexane (6×100 ml) at 60° C. and thendried under vacuum.

Ethylene Pre-polymerization

The catalyst component prepared according to the above procedure waspre-polymerized with ethylene to give a weight ratiopre-polymer/catalyst of 2.3 g/g. The pre-polymerization was carried outin hexane using TEAL as cocatalyst (weight ratio TEAL/cat 0.05).

Treatment Stage with the Ti Compound

The so obtained ethylene pre-polymer, was suspended in liquid TiCl₄ alsocontaining diisobutylphthalate. The amounts of reactants were such as togive a concentration of pre-polymer in the liquid phase of 60 g/l and anamount of diisobutylphthalate of 5% with respect to the prepolyrner. Thetemperature was then raised at 80° C. and the system was kept underthese conditions, with stirring, for 1 hour. After that time stirringwas discontinued the liquid siphoned off and the solid washed withhexane at 60° C. The titanation step was then repeated according to theabove procedure except for the omitted use of diisobutylphthalate andfor the shorter reaction time (30 min.).

Ethylene Copolymerization

A 15.0 liter stainless-steel fluidized reactor equipped withgas-circulation system, cyclone separator, thermal exchanger,temperature and pressure indicator, feeding line for ethylene, propane,1-butene, hydrogen, and a 1 L steel reactor for the catalystprepolymerization and injection of the prepolymer. The gas-phaseapparatus was purified by fluxing pure nitrogen at 40° C. for 12 hoursand then was circulated a propane (10 bar, partial pressure) mixturecontaining 1.5 g of TEAL at 80° C. for 30 minutes. It was thendepressurized and the reactor washed with pure propane, heated to 75° C.and finally loaded with propane (2 bar partial pressure), 1-butene (asreported in Table 4), ethylene (7.1 bar, partial pressure) and hydrogen(2.1 bar, partial pressure).

In a 100 mL three neck glass flask were introduced in the followingorder, 20 mL of anhydrous hexane, the amount of alkylaluminum reportedin table 7, 0.05 g of the prepolymerized catalyst andcyclohexylmethyl-dimethoxysilane in such an amount to give an Al/donormolar ratio of 15. They were mixed together and stirred at roomtemperature for 5 minutes and then introduced in the prepolymerizationreactor maintained in a propane flow. The autoclave was closed and 80 gof propane and 90 g of propene were introduced at 40° C. The mixture wasallowed stirring at 40° C. for 1 h. The autoclave was then depressurizedto eliminate the excess of non-reacted propene, and the obtainedprepolymer was injected into the gas-phase reactor by using a propaneoverpressure (1 bar increase in the gas-phase reactor). The finalpressure, in the fluidized reactor, was maintained constant during thepolymerization at 75° C. for 180 minutes by feeding a 10 wt. %1-butene/ethene mixture. At the end, the reactor was depressurised andthe temperature was dropped to 30° C. The collected polymer was dried at70° C. under a nitrogen flow and weighted.

The polymer characteristics are collected in Table 7.

TABLE 1 Alkyaluminum Melt Index 1-C₄- D. S. C. Catalyst m. Activity E FF/E (I.R.) Density Tc Tm ΔH X.S. Example Mg Type ratio mmol Kg/gcatDg/min dg/min wt. % g/ml ° C. ° C. J/g Wt. % Comp. 1 34.2 TEAL — 1010.06 0.74 33.9 45.8 10.4 0.9183 105.9 123.1 114.5 13.2 1 21.3 DMAC-TEAL  0.5 10 13.90 1.9 63.6 33.5 13.8 0.9051 104.6 122.4 92.0 21.3 2 19.4DMAC-TEAL 2 10 19.48 2.8 80.2 28.6 15.5 0.9076 104.7 122.5 95.8 24.8 323.4 DMAC-TEAL 1 10 17.95 2.4 67.2 28.0 13.3 0.9092 103.8 122.4 93.720.6 4 19.5 DMAC-TEAL 1 10 21.85 2.6 69.7 26.8 12.2 0.9100 102.8 122.098.0 21.3 5 19.3 DMAC-TEAL 1 10 17.25 2.5 78.2 31.3 13.7 0.9101 104.8122.4 95.6 23.3 6 19 DMAC-TEAL 1 10 14.89 3.5 150.0 42.9 15.9 101.4122.1 84.3 25.6 7 19 DMAC-TEAL 2 10 17.9 2.2 57.9 26.3 10.5 0.9146 104.9122.3 103.5 17.2 Comp. 2 87.5 DMAC — 20 2.2 0.11 3.2 29.1 9.8 0.9166 123103 17.2

TABLE 2 alkyaluminum α-olefin DSC Catalyst mol. α-olefin Activity (¹HNMR) Tc Tm □H Example mg Type ratio mmol Type Kg/gcat mol. % ° C. ° C.J/g Comp. 3 8.7 TEAL — 1.31 1-hexene 1.2 5.7 102.8 124.0 127.2 8 6.4DMAC/TEAL 1 ″ ″ 2.4 15.7 102.0 121.5 48 Comp. 4 6.1 TIBAL — ″ ″ 0.34 2.5103.0 126.8 129.3 9 9.7 DMAC/TIBAL 1 ″ ″ 1.4 19.0 100.8 121.6 34.1 Comp.5 7.1 TEAL — ″ 1-octene 1.9 2.5 104.9 128.9 122.4 10  4.2 DMAC/TEAL 1 ″″ 4.5 4.6 104.6 124.1 89.7

TABLE 3 DSC Cat. alkyaluminum α-olefin Polymer Activity I.V. C6-tot. Tm(II) □Hf Example mg Kind and molar ratio Mmol Type G g/gcat dl/g % molTc (° C.) (° C.) J/g Comp. 6 8.8 TEAL 1.31 1-hexene 9.43 1072 6.95 4.2104.1 125.7 137.8 11 8.3 TEAL/DMAC 1-1 1.31 ″ 16.32 1966 5.37 8.8 95.7122.1 104 12 8.5 ″ ″ ″ 16.52 1944 6.56 5.2 104.1 124.8 125.7 13 6 ″ ″ ″15.73 2622 3.97 6.9 99.5 123.2 93.4 Comp. 7 10.2 ″ ″ ″ 12.22 1198 6.713.6 103.8 126 123 14 10.4 ″ ″ ″ 16.06 1544 3.16 10.2 100.4 122.3 88.1

TABLE 4 Polymer Aluminumalkyl PC₂ ⁻ 1-Butene Kg/g 1-C₄ density DSCExample Kind and ratio g Al/Ti bar G G cat % w g/ml. Tc Tm (II) □H X.S.Comp 8 TEAL 0.96 1041 7 250 270 17.4 16.7 0.9156 103.1 122.5 86.4 26.215 TEAL/DMAC 1/1 0.87 1766 7 200 210 23.3 17.0 0.9040 103.6 124.0 95.030.1

TABLE 5 Aluminumalkyl PC₂ ⁻ 1-Butene Activity 1-C4 density Example Kindand ratio g bar g Kg/g cat % w g/ml. Comp 9 TEAL 0.96 7 150 14.4 16.70.9242 16 TEAL/DMAC 7/3 0.89 7 150 22.7 17.0 0.9093

TABLE 6 DSC^(§) Cat. Aluminumalkyl 1-C6- Polymer Activity I.V. 1-C₆ TcTm (II) □H Example mg Kind and ratio mmol ml G g/gcat dl/g % w (° C.) (°C.) J/g Comp 10 13.2 DIOA-H 1.31 30  4.36 330.3 2.7 8.0 106 125.9 108.417 9.3 DIOA-H/DMAC 1.31 30 15.25 1640 8.1 16.4 101 125.8 91.5

TABLE 7 Polymer Cat. Aluminumalkyl PC₂ ⁻ 1-Butene Kg/g 1-C4 Example MgKind and ratio Mmol bar g g cat % w 18 35 DIOAH/DMAC 1/1 8.42 8.4 166320 9.1 14.7

TABLE 8 Cat. Aluminumalkyl 1-C6- P C2- time polymer I.V. 1-C6-tot.Example mg Kind and ratio Mmol Ml Bar min g g/gcat dl/g % mol Comp. 115.5 TEA 1.31 10.0 5.0 60 28.6 5193 7.1 3.3 19 5.1 TEAL/DMAC 1-1 1.3110.0 5.0 60 27.1 5306 5.6 5.4

TABLE 9 DSC Cat. Aluminumalkyl 1-Butene Activity 1-C4 density □H X.S.Example mg Kind and ratio g Bar Kg/g cat % w g/ml J/g wt % Comp 12 0.05TEAL 0.96 2.3 15.4 7.5 0.9177 116.1 11 20 0.05 TEAL/DMAC 7/3 0.96 2.3 229.5 0.9163 120 17.8

What is claimed is:
 1. A catalyst system for the polymerization ofolefins CH₂═CHR, wherein R is hydrogen or a hydrocarbon radical having1-12 carbon atoms, comprising: (a) a solid catalyst component comprisingMg, Ti and halogen, and a co-catalyst mixture comprising (b)dimethylaluminium chloride and (c) an alkylaluminium compound wherein insaid mixture the compounds (b) and (c) are in a molar ratio (b)/(c)ranging between 0.3 and
 5. 2. The catalyst system according to claim 1,in which the ratio between (b) and (c) is between 0.3 and
 3. 3. Thecatalyst system according to claim 1, in which the alkylaluminium isselected from the compounds of formula AlR¹ _(3−y)H_(y) where y is from0 to 2 and R¹ is a hydrocarbon group having from 1 to 15 carbon atoms.4. The catalyst system according to claim 3, which the alkylaluminium isa trialkylaluminium selected from those of formula AlR¹ _(3−y)H_(y) inwhich y is 0 and R¹ is a C2-C10 alkyl radical.
 5. The catalyst systemaccording to claim 4, which the trialkylaluminium is triethylaluminiumor triisobutylaluminium.
 6. The catalyst system according to claim 1, inwhich the component (a) comprises a titanium compound supported on amagnesium chloride.
 7. The catalyst system according to claim 6, whichthe titanium compound is selected from those of formulaTi(OR²)_(n−y)X_(y) where X is chlorine, n is the valence of titanium, yis a number between 0 and n, and the R² groups, which may be the same ordifferent, are hydrocarbon radicals having from 1 to 10 carbon atoms. 8.The catalyst system according to claim 7, in which the titanium compoundis selected from TiCl₄, TiCl₃, titanium (IV) butoxide, titanium (IV)isopropoxide, trichlorobutoxytitanium (IV), or dichlorobutoxytitanium(III).
 9. The catalyst system according to claim 1 further comprising aninternal electron donor compound.
 10. The catalyst system according toclaim 9 in which the internal electron donor compound is selected fromalkyl, cycloalkyl or aryl esters of polycarboxylic acids.
 11. Thecatalyst system according to claim 10 in which the esters ofpolycarboxylic acids are phthalates or succinates.
 12. The catalystsystem according to claim 1 in which the component (a) is obtained byreacting a titanium compound selected from those of formulaTi(OR²)_(n−y)X_(y), where X is chlorine, n is the valence of titanium, yis a number between 0 and n, and the R² groups, which may be the same ordifferent, are hydrocarbon radicals having from 1 to 10 carbon atoms,with a magnesium chloride derived from an adduct of formula MgCl₂.pROH,where p is a number between 0.1 and 6, and R is a hydrocarbon radicalhaving 1-18 carbon atoms.
 13. The catalyst system according to claim 12having a surface area (by the B.E.T. method) from 20 and 500 m²/g, and aporosity (Hg method) due to pores with a radius up to 10,000 Å from 0.3to 1.5 cm³/g.
 14. The catalyst system according to claim 1, obtained byfirst placing the components (a) and (c) in contact and then reactingthe product thus obtained with the component (b).
 15. The catalystsystem according to claim 1, obtained by placing the component (a) incontact with the cocatalyst mixture of (b) and (c).
 16. The catalystsystem according to claim 1, obtained by first placing the components(a) and (b) in contact and then reacting the product thus obtained withthe component (c).
 17. The catalyst system according to claim 1 whereinthe catalyst component (a) is pre-polymerized with at least one ofethylene and α-olefins.
 18. The catalyst system according to claim 17wherein the catalyst component (a) is pre-polymerized with ethylene upto forming amounts of polymer from about 0.1 g per gram of solidcomponent up to about 100 g per gram of solid catalyst component. 19.The catalyst system according to claim 17 herein the pre-polymerizedcatalyst component is further treated with TiCl₄ before being used inthe main polymerization step.
 20. The catalyst system according to claim12, where p is a number between 2 and 3.5.
 21. A process for thepolymerization of olefins CH₂═CHR, wherein R is hydrogen or ahydrocarbon radical having 1-12 carbon atoms, carried out in thepresence of a catalyst system for the polymerization of olefins CH₂═CHR,wherein R is hydrogen or a hydrocarbon radical having 1-12 carbon atoms,comprising: (a) a solid catalyst component comprising Mg, Ti andhalogen, and a co-catalyst mixture comprising (b) dimethylaluminiumchloride and (c) an alkylaluminium compound wherein in said mixture thecompounds (b) and (c) are in a molar ratio (b)/(c) ranging between 0.3and
 5. 22. A process for the preparation of copolymers of ethylene withone or more alpha-olefins having from 3 to 12 carbon atoms, having amole content of units derived from the ethylene of higher than 80%,wherein the polymerization of ethylene and said alpha-olefins is carriedout in the presence of a catalyst system for the polymerization ofolefins CH₂═CHR, wherein R is hydrogen or a hydrocarbon radical having1-12 carbon atoms, comprising: (a) a solid catalyst component comprisingMg, Ti and halogen, and a co-catalyst mixture comprising (b)dimethylaluminium chloride and (c) an alkylaluminium compound wherein insaid mixture the compounds (b) and (c) are in a molar ratio (b)/(c)ranging between 0.3 and
 5. 23. The process according to claim 21 carriedout in the gas phase.
 24. The process according to claim 22 carried outin gas-phase.